imposition

The plan of arrangement of the pages of type in a
chase so that they will read consecutively when
the printed sheet is folded. It is a term which
means literally "in position," and originated in
letterpress printing.

There are four standard methods of imposition: 1)
sheetwise; 2) work-and-turn; 3) work-and-tumble;
and 4) work-and-twist. The purpose of having
different schemes is to obtain maximum economy in
printing.

Sheetwise imposition, also known as
"work-and-back," "front-and-back," or
"print-and-back," requires two image carriers per
color, one each for the front and back of the
sheet. This method is used for printing jobs where
the number of pages to be printed on each side of
the sheet is large enough to utilize the full
capacity of the press.

Work-and-turn imposition, also known as
"print-and-turn," is used where it is practical to
print both sides of the sheet from a single image
carrier per color. It is frequently used, and
requires relatively large presses because the
sheet will carry two complete units, each
occupying one-half of the sheet. The sheet is
either slit during backup or is cut apart after
printing. Workand-turn imposition cuts the number
of sheets to be printed by 50%, but it generally
requires larger and more expensive presses than
sheetwise imposition.

Work-and-tumble imposition, also known as
"print-and-tumble," "workand-roll," or
"work-and-flop," is used less frequently than
either of the two previous methods. It is selected
when a work-and-turn form cannot be used, or when
two sheetwise forms would have to be run on a
sheet of difficult dimensions. This method needs
only one image carrier for printing both sides of
the sheet, and in this respect it is similar to
work-and-turn.

Work-and-twist imposition, also known as
"work-and-twirl," differs fundamentally from all
three previous schemes. While the first three are
methods designed to produce sheets printed on both
sides, work-and-twist imposition solves problems
pertaining to one-side printing, e.g., printing
blank rule and tabular forms, with cross rules in
one section and vertical rules in the other. In
this method, two separate sections, or divisions,
of an individual form are imposed and locked up
together in such a manner that they may be printed
side by side on a double-sized sheet in one
impression. After completion of the run, the
already printed paper is repositioned face up for
the second printing from the same image carrier.
Work-and-twist imposition is actually rarely used,
as it requires nearly perfectly square stock for
execution. (234 ,
287 , 289 , 316 , 320 , 339 )